This U.S. non-provisional application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 2003-12044, filed on Feb. 26, 2003, in the Korean Intellectual Property Office, the contents of which are incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to film formation in the manufacturing of metal-insulator-metal (MIM) capacitors.
2. Description of the Related Art
Recently, due to their excellent electrical properties (such as resistivity), ruthenium and ruthenium compounds are being used as thin film electrode materials in the production of semiconductor devices for Dynamic Random Access Memory (DRAM) and Ferroelectric Random Access Memory (FeRAM).
Ruthenium or ruthenium compound films are usually formed by sputtering or chemical vapor deposition (CVD) methods. In particular, CVD is preferred since thin layers with uniform thickness are easily formed.
In order to form ruthenium films using CVD, a ruthenium source is required. Currently, bis(ethylcyclopentadienyl)ruthenium [Ru(EtCp)2], as shown in FIG. 1, is the most common ruthenium source. Such an organic ruthenium compound is obtained by replacing one hydrogen on each of two cyclopentadiene rings of bis(cyclopentadienyl)ruthenium with an ethyl group. Because the bis(ethylcyclopentadienyl)ruthenium has a low melting point, it is a liquid at room temperature. Therefore, bis(ethylcyclopentadienyl)ruthenium possesses good handling properties.
However, the bis(ethylcyclopentadienyl)ruthenium has problems in its use as a material for ruthenium films. The main problem is that it is difficult to carry out the nucleation of the bis(ethylcyclopentadienyl)ruthenium. In order to solve this problem, ruthenium films are generally formed under increased oxygen flow rate and deposition pressure. However, if the oxygen flow rate and the deposition pressure are increased, the nucleation rate per unit area is excessively increased. As a result, ruthenium films form in a needle shape. Formation of such needle-shaped ruthenium films results in surface morphology, increase of a sheet resistance, and generation of a leakage current. On the other hand, if ruthenium films are formed under decreased deposition pressure and oxygen flow rate, the nucleation rate is excessively lowered. As a result, ruthenium grains are separated from each other.
Due to this problem, when bis(ethylcyclopentadienyl)ruthenium is used as the ruthenium source for forming films, ruthenium films may sometimes be formed using a method comprising (a) carrying out nucleation of the bis(ethylcyclopentadienyl)ruthenium under increased oxygen flow rate and deposition pressure and (b) depositing the ruthenium films under decreased oxygen rate and deposition pressure. In this case, however, due to the different process conditions used, the process burden is increased. In addition, if the two steps are carried out in-situ, the process conditions become unstable during the transitional stage between the two steps. As a result, the reproducibility and reliability of the process are lowered. On the other hand, if the two steps are carried out in two separate chambers, a residue may be left on the surface of a wafer when the wafer is transferred from one chamber to the other. In addition, when a gas for cooling the wafer is introduced into a chamber, the wafer is often displaced due to the change in pressure. As a result, the ruthenium films on the wafer do not have uniform thickness.
Meanwhile, the bis(ethylcyclopentadienyl)ruthenium has another problem in that ruthenium films made of bis(ethylcyclopentadienyl)ruthenium have relatively low adhesion to silicon dioxide films which are commonly used as interlayer insulating layers.